The present invention relates to plate-, foil- or strip-shape support materials for offset printing plates, wherein the materials are based on aluminum having a hydrophilic coating. The present invention also relates to a process for the manufacture of these materials, and to the use of the materials in the preparation of offset printing plates.
Support materials for offset printing plates, prepared either by the consumer directly or by the manufacturer of pre-coated printing plates, are provided on one or both sides with a light-sensitive layer (copying layer), with the aid of which an image of an original is photomechanically produced. When the printing form has been prepared, the support carries the ink-receptive image areas and at the same time forms, in the image-free areas (non-image areas), the water-receptive image background for the lithographic printing process.
A support for light-sensitive material for preparing lithographic plates therefore must meet the following requirements:
The parts of the light-sensitive layer which have become relatively more soluble after exposure must be readily removable from the support by developing, without leaving a residue, in order to produce the hydrophilic non-image areas.
The support bared in the non-image areas must have great affinity for water, i.e., it must be strongly hydrophilic, to take up water rapidly and permanently in the lithographic printing process and to have an adequate repellent effect toward the oily printing ink.
The light-sensitive layer before exposure and the printing parts of the layer after exposure must adhere to a sufficient extent to the support.
The base material used for supports of this type can be aluminum, steel, copper, brass or zinc foils, and in addition, also plastic film or paper. These raw materials can be converted into supports for offset printing plates, for example, by graining, dull chromium plating, surface oxidation and/or application of an intermediate layer. Aluminum, today probably the most frequently used base material for offset printing plates, is surface-roughened by known methods using dry brushing, wet brushing, sand blasting or chemical and/or electrochemical treatment. To increase the abrasion resistance, the roughened substrate can be additionally subjected to an anodizing step to build up a thin oxide layer.
In practice, the support materials, in particular anodically oxidized support materials based on aluminum, are in many cases subjected to a further treatment step before application of a light-sensitive layer, in order to improve the layer adhesion, to increase the hydrophilic character and/or to facilitate the developability of the light-sensitive layers. These treatment steps include, for example, the following methods:
In German Pat. No. 907,147 (=U.S. Pat. No. 2,714,066), German Auslegeschrift No. 1,471,707 (=U.S. Pat. Nos. 3,181,461 and 3,280,734) or German Offenlegungsschrift No. 2,532,769 (=U.S. Pat. No. 3,902,976), processes are described for rendering hydrophilic printing plate support materials based on optionally anodically oxidized aluminum. In those processes, the materials are treated with aqueous sodium silicate solution, either without or with the use of electric current.
It is known from German Pat. No. 1,134,093 (=U.S. Pat. No. 3,276,868) and German Pat. No. 1,621,478 (=U.S. Pat. No. 4,153,461), to use polyvinylphosphonic acid or copolymers based on vinylphosphonic acid, acrylic acid and vinyl acetate to render hydrophilic printing plate support materials based on optionally anodically oxidized aluminum. The use of salts of these compounds is also mentioned but not specified in more detail.
The use of complex fluorides of titanium, zirconium or hafnium, in accordance with German Auslegeschrift No. 1,300,415 (=U.S. Pat. No. 3,440,050), also additionally renders hydrophilic aluminum oxide layers on printing plate support materials.
In addition to these hydrophilizing methods which have become particularly well known, the use of, for example, the following polymers in this area of application has also been described:
German Auslegeschrift No. 1,056,931 describes the use of water-soluble, linear copolymers based on alkyl vinyl ethers and maleic anhydrides in light-sensitive layers for printing plates. Of these copolymers, particularly hydrophilic are those in which the maleic anhydride component is reacted incompletely, or more or less completely, with ammonia, an alkali metal hydroxide or an alcohol.
German Auslegeschrift No. 1,091,433 describes how printing plate support materials based on metals are rendered hydrophilic by means of film-forming organic polymers such as polymethacrylic acid or sodium carboxymethylcellulose or sodium hydroxyethylcellulose, in the case of aluminum supports, or by means of copolymers of methyl vinyl ether and maleic anhydride, in the case of magnesium supports.
To render hydrophilic printing plate support materials made of metals, in accordance with German Auslegeschrift No. 1,173,917 (=British Pat. No. 907,718), initially water-soluble polyfunctional amino-urea-aldehyde synthetic resins or sulfonated urea-aldehyde synthetic resins are used, which are then hardened on the metal support to form a water-insoluble state.
To prepare a hydrophilic layer on printing plate support materials, according to German Auslegeschrfit No. 1,200,847 (=U.S. Pat. No. 3,232,783), first (a) an aqueous dispersion of a modified urea-formaldehyde resin of an alkylated methylol-melamine resin or of a melamine-formaldehydepolyalkylenepolyamine resin is applied to the support, whereupon (b) an aqueous dispersion of a polyhydroxy or polycarboxy compound such as sodium carboxymethylcellulose is applied, and finally the substrate thus coated is (c) treated with an aqueous solution of a Zr, Hf, Ti or Th salt.
German Auslegeschrift No. 1,257,170 (=U.S. Pat. No. 2,991,204) describes, as an agent for rendering printing plate support materials hydrophilic, a copolymer which, in addition to acrylic acid, acrylate, acrylamide or methacrylamide units, also contains Si-trisubstituted vinylsilane units.
German Offenlegungsschrift No. 1,471,706 (=U.S. Pat. No. 3,298,852) describes the use of polyacrylic acid as an agent for rendering hydrophilic printing plate support materials made of aluminum, copper or zinc.
The hydrophilic layer on a printing plate support material in accordance with German Pat. No. 2,107,901 (=U.S. Pat. No. 3,733,200) is formed from a water-insoluble hydyrophilic acrylate or methacrylate homopolymer or copolymer having a water absorption of at least 20% by weight.
To densify anodically oxidized aluminum surfaces, according to German Offenlegungsschrift No. 2,211,553 (=U.S. Pat. No. 3,900,370), a process is used in which, at a temperature of at least 90.degree. C. and at a pH value of 5 to 6.5, a solution is applied which contains water-soluble phosponic acids which form complexes with divalent metals, or salts of these acids (such as 1-hydroxyethane-1,1-diphosphonic acid or aminotrimethylenephosphonic acid), and Ca.sup.2+ ions; these solutions can also additionally contain dextrins.
German Auslegeschrift No. 2,305,231 (=British Pat. No. 1,414,575) describes a method for rendering hydrophilic printing plate support materials in which method a solution or dispersion of a mixture of an aldehyde and of a synthetic polyacrylamide is applied to the support.
German Offenlegungsschrift No. 2,308,196 (=U.S. Pat. No. 3,861,917) describes a method for rendering hydrophilic roughened and anodically oxidized aluminum printing plate supports by using ethylene- or methyl vinyl ether-maleic anhydride copolymers, polyacrylic acid, carboxymethylcellulose, sodium poly(vinylbenzene-2,4-disulfonic acid) or polyacrylamide.
German Auslegeschrift No. 2,364,177 (=U.S. Pat. No. 3,860,426) describes a hydrophilic adhesive layer for aluminum offset printing plates which is arranged between the anodically oxidized surface of the printing plate support and the light-sensitive layer and which, in addition to a cellulose ether, additionally contains a water-soluble Zn, Ca, Mg, Ba, Sr, Co or Mn salt. The layer weight of the cellulose ether in the hydrophilic adhesive layer is 0.2 to 1.1 mg/dm.sup.2, the same layer weight being indicated also for the water-soluble salts. The mixture of cellulose ether and salt is applied to the support in aqueous solution, optionally with the addition of an organic solvent and/or a surfactant.
To densify anodically oxidized aluminum surfaces, according to U.S. Pat. No. 3,672,966, after the surfaces have been sealed, aqueous solutions of acrylic acid, polyacrylic acid, polymethacrylic acid, polymaleic acid or copolymers of maleic acid with ethylene or vinyl alcohol are used.
According to U.S. Pat. No. 4,049,746, the agents used for rendering hydrophilic printing plate support materials contain salt-like products obtained from reacting water-soluble polyacrylic resins having carboxyl groups with polyalkyleneimine-urea-aldehyde resins.
British Pat. No. 1,246,696 describes, as agents for rendering hydrophilic anodically oxidized aluminum printing plate supports, hydrophilic colloids such as hydroxyethylcellulose, polyacrylamide, polyethylene oxide, polyvinylpyrrolidone, starch or gum arabic.
Japanese Preliminary Published Application No. 64/23,982 describes how metal printing plate supports are rendered hydrophilic by means of polyvinylbenzenesulfonic acid.
For use in rendering hydrophilic printing plate support materials, the state of the art also describes metal complexes which are such that they have low-molecular ligands and include, for example:
complex ions of divalent or polyvalent metal cations and ligands such as ammonia, water, ethylenediamine, nitrogen oxide, urea or ethylenediamine tetraacetate, according to German Offenlegungsschrift No. 2,807,396 (=U.S. Pat. No. 4,208,212),
ferric cyanide complexes, such as K.sub.4 [Fe(CN).sub.6 ] or Na.sub.3 [Fe(CN).sub.6 ], in the presence of heteropoly acids, such as phosphomolybdic acid, or their salts and of phosphates, according to U.S. Pat. No. 3,769,043 or
ferric cyanide complexes in the presence of phosphates and complex formers such as ethylenediamine tetraacetic acid for electrophotographic printing plates having a zinc oxide surface, according to Dutch Preliminary Published Application No. 68/09,658 (=U.S. Pat. No. 3,672,885).
However, all the methods described above have more or less great disadvantages, so that the resulting support materials in many cases no longer satisfy current offset printing requirements for the following reasons:
Thus, after the treatment with alkali metal silicates, which lead to good developability and hydrophilic character, a certain deterioration of the shelf life of light-sensitive layers applied thereto must be accepted.
Although the complexes of transition metals, in principle, enhance the hydrophilic character of anodically oxidized aluminum surfaces, the complexes have the disadvantage that they are very readily soluble in water, with the result that they can be readily removed when the layer is developed with aqueous developer systems which of late contain to an increasing extent surfactants and/or chelating agents which have high affinity for these metals. This more or less strongly reduces the concentration of transition metal complexes on the surface and can thus lead to attenuation of the hydrophilic effect.
In the treatment of supports with water-soluble polymers, the ready solubility of the latter, particularly in aqueous alkaline developers of the type predominantly used for developing positive-working light-sensitive layers, likewise causes marked attenuation of the hydrophilicity-imparting effect.
In the case of polymers containing carboxylic acid groups, the fact that free carboxylate functions can interact with the diazo cations of negative-working light-sensitive layers has a noticeable adverse effect, so that, after developing with developers containing organic solvents, a marked yellow haze due to retained diazo compounds remains in the non-image areas.
The combination of a mixture of a water-soluble polymer, such as a cellulose ether, and a water-soluble metal salt also leads to reduced adhesion of the layer, since the layer weights and hence the layer thickness are chosen to be relatively high (see German Auslegeschrift No. 2,364,177). This can manifest itself, for example, by the fact that, in developing, some of the developer liquid migrates underneath image areas.